2013-04-18_PERMIT FILE - C2009087A

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RULE 2 - PERMITS • In general, all three bedrock units tested in bedrock wells included with the PSCM baseline hydrology monitoring program exhibited very low hydraulic conductivities and transmissivities typical of fine- to very fine- grained sedimentary rocks. The hydraulic conductivities at the COV23 -CW23 -CWU23 well set were an order of magnitude higher (Oldaker, 2009) because of the larger values at COV23 and CWU23. Transmissivity values, the product of the hydraulic conductivity multiplied by the saturated thickness of the aquifer, were also very small, ranging from 0.005 to 1.1 feet squared per day (ft /d). Earlier aquifer tests conducted by the U.S. Geological Survey and summarized in Robson and Stewart (1990) and Williams and Clark (1994) indicated larger hydraulic conductivity values for the overburden, Wadge Coal, and underburden near the areas mined as part of the Seneca operations. Testing at the Spring Creek site of Williams and Clark, near the proposed PSCM portal area, gave values of 0.2, 0.9 and 0.6 ft/d, respectively, for the overburden, Wadge Coal and underburden, and testing at the Cow Camp site of Williams and Clark, in the southeast part of the PSCM permit area, gave values of 0.1,1 and 8 ft/d for the respective units. Both sites are adjacent to mined areas. Reported values away from mined areas (the Zuli and Bond Creek sites of Williams and Clark, 1994) were 0.03 and 5 ft/d for overburden, 0.3 and 0.002 ft/d for Wadge coal, and 0.00006 and 0.001 ft/d for underburden. Williams and Clark (1994) attributed the larger hydraulic conductivities near the mined areas to the fact that the aquifers there are at much shallower depths, under less confining pressure from overlying rocks, and therefore are more fractured. In down - dip areas, the units have lower hydraulic conductivities because they are at greater depths • and are therefore under greater pressure from the overlying rocks, exhibit fewer fractures, and are not subject to secondary permeability resulting from mining activity. Williams and Clark (1994) also suggested that mining activity such as blasting and heavy equipment movement may have caused secondary porosity in the bedrock aquifers and increased their hydraulic conductivities. Spoils aquifer tests discussed by Robson and Stewart (1990) and Williams and Clark (1994) indicated that the spoils aquifer had a hydraulic conductivity ranging from 60 to 500 ft/d. The much higher hydraulic conductivity of the spoils compared to the adjacent undisturbed bedrock units results in formation of the saturated zone in the spoils, because the bedrock cannot transmit the spoils aquifer recharge away from the mined area as quickly as it accumulates in the spoils. The volumetric flow of groundwater through the PSCM permit area under pre- mining conditions can be estimated by applying Darcy's law using the hydraulic properties discussed above and the hydraulic gradients. For the bedrock units, the hydraulic properties discussed above can be used, and the hydraulic gradients can be based on the potentiometric surface elevation maps presented in Figures 2.04.7 45, 2.04.7 -F6 and 2.04.7 -F7. For the alluvial aquifers in the Grassy Creek and Little Grassy Creek valleys, the hydraulic properties and gradients can be estimated from literature values and land - surface slopes, respectively. The equation for volumetric flow (Freeze and Cherry, 1979) is: • Q =T•I•W where: Q = volumetric flow rate PSCM Permit App. 2.04 -49 Revision 03/05/10